Just head to Settings > Data and Storage > Storage Usage and try one (or all
1) Set up Auto-Remove to clear cached media after a certain period with separate settings for Private Chats, Groups and Channels – and exceptions for individual chats.
2) Set a maximum cache size – if your cache reaches this limit, the oldest media will be removed.
3) Find the largest media items with dedicated tabs and detailed pie charts and manually clear them from your cache or select specific chats that take too much space.